We use rich:dropDownMenu with attributes disabled and styleClass. But when disabled is true then styleClass is not applied. Using classes for styling via CSS is a must, also for disabled components.
Comment from attribute styleClass: "Space-separated list of CSS style class(es) to be applied when this element is rendered."
Also a disabled component may be rendered (otherwise styling wont matter).
It is easy to fix. How to:
DropDownMenuRenderer.doEncodeEnd(...) contains following line:
String value = "rf-ddm-lbl " + convertToString((isDisabled ? "rf-ddm-dis" : ("rf-ddm-unsel " + styleClass))) + " ";
If component is disabled styleClass must be added also.